Now to the battle against Isis. The president returns to Washington tonight. The white house weighing a dramatic expansion of air strikes. Using the ominous words "Imminent threat." We begin with the latest on the hunt for the killers of American James Foley. Here's Brian Ross, ABC's chief investigative correspondent. Reporter: A gruesome, heartbreaking videotape. His last words were, I wish I had more time. To see my family. Reporter: A failed hostage rescue attempt inside Syria. It turned out the hostages were no longer at that location. Reporter: And a worldwide wakeup call about an islamist terrorist group said to be more extreme than Al Qaeda. No just god would stand for what they did yesterday and what they do every single day. Reporter: And in one week's time, the threat from the terror group kauped Isis no longer seems limbed to far. Away Iraq and Syria. In a bulletin Friday, homeland security says Isis supporters are calling for attacks inside the U.S., though there are no credible threats at this time. So, yes, they are an imminent threat to every interest we have, with whether it's in Iraq or anywhere else. Reporter: The hooded killer who beheaded James Foley is believed to be a british citizen. And the FBI is now using a database of known british jihadists to look for a match with his eyes, his hands, and his voice with its distinctive London accent. You have plotted against us. Reporter: This morning, growing fear about a second American hostage. 31-year-old journalist Steven sotloff. The U.S. Has said it would not negotiate nor pay ransom for any Americans held by Isis. We don't provide funding for terrorist investigations. Reporter: Former FBI agent jack Cloonan helped to negotiate the release of one european hostage from Isis. He says the U.S. Policy needs to be re-examined. Any of us in the position of the foleys or others would say, I want the opportunity to saved my loved one. Reporter: But in the case of James Foley, the ransom demand was an absurd $130 million. That means they're using the American hostages for something other than money. This is game of revenge. And revenge is sweet to them. Reporter: In his final moments, Jim Foley faced death with the dignity and courage that marked his journalistic career. Brian Ross, ABC news, New York. Thanks to Brian for that. We're going to turn to the military options. The U.S. Has hit Isis with nearly 100 air strikes inside Iraq. The big question now -- should the U.S. Strike inside Syria. Alex Marquardt has the latest. Reporter: The front line in the fight against Isis. On one bank of this canal, kurdish fighters. On the other, Isis militants. You see the building over there? Reporter: Yeah. The small structure there. They're watching you. Reporter: They're watching us right now. You see the hole. Reporter: Yeah. He's standing there watching you. You see the head? Reporter: These kurds tell us they're the best hope of pushing back and defeating Isis, but need more American weapons and air strikes. The U.S. Has carried out more than 100 air strikes in support of kurdish and Iraqi forces. As a result, Isis has lost some ground. Including the prized mosul dam. But Isis still controls an enormous swath of land, about the size of Indiana, stretching from western Iraq into eastern Syria. They have hundreds of millions of dollars, heavy weaponry, and their ranks are growing by the day. Now estimated at 10,000 fighters, around 100 Americans included. This is beyond anything we have seen. So we must prepare for everything. And the only way you do that is you take a cold, steely, hard look at it and get ready. Reporter: Getting ready now means possibly expanding the U.S. Operation for the first time into Syria, where Isis has its head quarters. The next step in what U.S. Officials warn will be a very long fight against Isis. George? Okay, Alex, thank you very much.

This transcript has been automatically generated and may not be 100% accurate.

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